Effects of Tetramethylpyrazine on Ang Ⅱ-induced Cardiomyocyte Hypertrophy and the Underlying Mechanisms

Abstract:

Objective: To investigate the inhibitory effects of tetramethylpyrazinee(TMP) on angiotensin Ⅱ (Ang Ⅱ)-induced cardiomyocyte hypertrophy and the underlying mechanisms. Method: Ang Ⅱ-induced cardiomyocyte hypertrophy model was established in isolated neonatal rat ventricular myocytes. The cells were then randomly divided into 6 groups:control group, Ang Ⅱ (0.1 μmol·L^-1) group, low-dose TMP (0.01 mmol·L^-1) group, middle-dose TMP (0.1 mmol·L^-1) group, high-dose TMP (1 mmol·L^-1) group, pyrolidine dithiocarbamate(PDTC, a NF-κB inhibitor, 100 μmol·L^-1) group. After 24 h treatment, cardiomyocytes were harvested to measure total protein content by Lowry's method, β-myosin heavy chain (β-MHC) mRNA expression by Real-time PCR, and NF-κB content by Western blotting. Result: Ang Ⅱ induced cardiomyocyte hypertrophy characterized by increased total protein content [Ang Ⅱ groupg(296.7±27.6) mg·L^-1;control group(184.3±11.6) mg L^-1,P<0.05]·L^-1;control group(184.3±11.6) mg·L^-1,P<0.05] and enhanced β-MHC mRNA expression (Ang Ⅱ group 0.936±0.059;control group 0.496±0.030,P<0.05), while TMP significantly inhibited Ang Ⅱ-induced hypertrophic growth in a dose-dependent manner. Meanwhile, TMP (1 mmol·L^-1) also attenuated Ang Ⅱ-induced increase in phosphorylated NF-κB (Ang Ⅱ group 0.861±0.065;TMP group 0.655±0.052,P<0.05) and I-κB protein content (Ang Ⅱ group 0.785±0.042;TMP group 0.525±0.045,P<0.05) in cardiomyocytes. Furthermore, inhibition of NF-κB by the specific inhibitor PDTC markedly suppressed Ang Ⅱ-induced hypertrophic responses. Conclusion: Our findings suggested that TMP inhibits Ang Ⅱ-induced cardiomyocyte hypertrophy through suppression of NF-κB pathway, which might contribute to the protective role of TMP in cardiac diseases.